A hybrid system and method for conditioning air for an enclosed space can include a direct cooling system in combination with an indirect cooling system. The hybrid system can use direct cooling when ambient temperature and humidity levels are such that 100% outdoor air can be delivered to the enclosed space. The hybrid system can use indirect cooling when 100% of the return air can be conditioned using an external cooling unit and then returned to the enclosed space as supply air. The external cooling unit can include an evaporative cooler and operate in a dry mode and a wet mode. The external cooling unit can produce a reduced temperature cooling fluid and provide liquid cooling to the air when the system is operating in the indirect mode, and in some cases, in the direct mode. The hybrid system can operate in a mixed mode in which the external cooling unit is off and a mix of return air and outdoor air can be delivered to the enclosed space.